This invention relates to pigment dispersing resins which are conveniently applicable to water-based paint, in particular, water-based automotive finish; and also to water-based pigment dispersions and water-based paint compositions which contain said pigment dispersing resin.
As paint for automotive finish, heretofore those of solvent-based type have been widely used, in which a base resin (base polymer) component such as acrylic resin, polyester resin or alkyd resin having such functional groups as hydroxyl and carboxyl groups; and a curing agent such as amino resin, optionally blocked polyisocyanate compound, epoxy compound and the like are concurrently used.
For the protection of terrestrial environment, paint of low volatile organic matter content (VOC) is demanded in these years. In the field of paint for automotive finish, switching to water-based paint of, in particular, colored base coating paint whose VOC discharge is high has been strongly required, and it is expected that replacement of solvent-based coating with water-based coating will proceed hereafter.
Problems incidental to the switching are, for example: (1) pigment dispersing resin blended in water-based paint is incompatible with the binder component in water-based paint; (2) pigment dispersing resin or dispersant fail to uniformly disperse the pigment and invite flocculation or agglomeration of the pigment; and (3) the pigment dispersing resin or dispersant in the water-based paint composition fail to cure under baking and invite degradation of the coating film performance.
Those pigments used for colored base coating paint generally have hydrophobic surfaces and are difficult to be water-wettable, while pigment dispersing resins conventionally used for solvent-based colored paints have low solubility in water and are inferior in dispersing stability in aqueous media. Hence it is important in designing a pigment dispersing resin for water-based paint, to secure satisfactory levels of both wettability of pigment and dispersing stability of the pigment dispersing resin in an aqueous medium.
Low viscosity and low molecular weight of pigment dispersing resin are considered advantageous for wetting property of pigment; and easy formation of steric repelling layer on the pigment surfaces or good solubility of the pigment dispersing resin in the continuous phase (aqueous medium) are considered advantageous for the dispersing stability. Both the pigment-wetting property and the dispersing stability of the pigment dispersing resin are considered to participate in wetting of the pigment surface with the pigment dispersing resin (a resin having a group capable of forming weak flocculation in aqueous system such as alkyl-group is effective) and in adsorption onto the pigment, which are attributable to the interaction between hydrophobic part on the pigment surface and that of pigment dispersing resin.
Past development of pigment dispersing resins or assistant for water-based paint has been advanced based on the foregoing viewpoints. For instance, Sho 50 (1975)-154328A-JP proposed use of a straight chain anionic polymer containing acidic functional groups which is obtained through polymerization of a monomer mixture containing as a part of its monomer components an acidic functional group-containing, polymerizable unsaturated monomer such as (meth)acrylic acid, as the pigment dispersing resin. Said polymer, however, exhibits high solubility in aqueous media and hence is unsatisfactory in respect of wetting of pigment. Furthermore, pigment dispersions formed with the use of said polymer show excessively high viscosity and are subject to a drawback of difficult handling
Hei 1 (1989)-182304A1-JP, Canadian Patent 2149399 and U.S. Pat. No. 5231131 disclosed, as the pigment dispersing resin, a graft copolymer obtained through copolymerization of carboxyl-containing macromonomers. Said graft copolymer excels in pigment dispersing stability because its trunk portion is hydrophobic and the branch portion is hydrophilic. Whereas, pigment dispersions formed with the use of said copolymer show high viscosity, and the graft copolymer is far from being satisfactory, in view of the increasing demand for pigment dispersions having high pigment concentration to save cost and to reduce VOC.
On the other hand, top coating paints for automotive finish are required not only high film performance such as durability, acid resistance, washability (scratch resistance) and chip resistance, but also still better appearance of coated film in sharpness, transparency, color development and the like.
An object of the present invention is to provide pigment dispersing resins which excel in wetting property and dispersing stability even at high pigment concentration and which can provide aqueous pigment dispersions of low viscosity and excellent color developing property.
A further object of the present invention is to provide a water-based pigment dispersion which has low viscosity even at high pigment concentration and which excels in color-developing property.
Another object of the invention is to provide a water-based paint which excels in curability and is capable of forming a painted film of splendid finish appearance in sharpness, transparency, color-developing property and the like.
Still other objects and characteristics of the invention will become apparent from the following descriptions.
We have engaged in extensive research work with the view to fulfill the above objects, to come to discover that a copolymer of a high acid value macromonomer which is obtained through copolymerization of specific monomeric components including methacrylic acid in the presence of a metal complex which is a catalytic chain transfer agent or an addition cleavage-type chain transfer agent, and optionally a radical-polymerization initiator, or this macromonomer into which a polymerizable unsaturated group is further introduced, with an ethylenically unsaturated monomer; and said copolymer into which further a long-chain alkyl group is introduced; are very suitable as pigment dispersing resins to be used in water-based paint. The present invention is thus completed
Thus, the invention provides a pigment dispersing resin which is obtained by copolymerizing
a macromonomer (A) having a resin acid value of 50-450 mgKOH/g, which is obtained by copolymerizing methacrylic acid with at least one copolymerizable monomer selected from methacrylic acid esters and styrene in the presence of a metal complex which is a catalytic chain transfer agent or an addition cleavage-type chain transfer agent and optionally a radical polymerization initiator, with
an ethylenically unsaturated monomer (B).
said resin having a weight-average molecular weight within a range of 3,000-100,000 and a resin acid value within a range of 10-200 mgKOH/g. (This resin is hereinafter referred to as xe2x80x9cpigment dispersing resin Ixe2x80x9d.)
The invention also provides a pigment dispersing resin having a weight-average molecular weight within a rang of 5,000-100,000 and a resin acid value within a range of 10-200 mgKOH/g, which is obtained by copolymerizing a macromonomer (A-1) provided by subjecting above macromonomer (A) to an esterification reaction with an epoxy-containing polymerizable unsaturated compound (C) whereby introducing a polymerizable unsaturated group into the former, with an ethylenically unsaturated monomer (B). (This resin is hereinafter referred to as xe2x80x9cpigment dispersing resin IIxe2x80x9d.)
The invention further provides a pigment dispersing resin having a weight-average molecular weight within a range of 3,000-100,000 and a resin acid value within a range of 10-200 mgKOH/g, which is obtained by copolymerizing
a macromonomer (A-2) provided by subjecting the macromonomer (A) to an esterification reaction with an epoxy-containing long chain alkyl compound (I)), whereby introducing the long chain alkyl group into the former, with
an ethylenically unsaturated monomer (B). (This resin is hereinafter referred to as xe2x80x9cpigment dispersing resin IIIxe2x80x9d.)
The invention also provides a pigment dispersing resin having a weight-average molecular weight within a range of 3,000-100,000 and a resin acid value within a range of 10-200 mgKOH/g, which is obtained by the steps of copolymerizing the macromonomer (A) with an ethylenically unsaturated monomer (B) to form a copolymer (E), and subjecting said copolymer (E) to an esterification reaction with an epoxy-containing long chain alkyl compound (D). (This resin is hereinafter referred to as xe2x80x9cpigment dispersing resin IVxe2x80x9d.)
The invention furthermore provides a pigment dispersing resin having a weight-average molecular weight within a range of 3,000-100,000 and a resin acid value within a range of 10-200 mgKOH/g, which is obtained by copolymerizing
a macromonomer (A-3) provided by subjecting said macromonomer (A) to an esterification reaction with an epoxy-containing polymerizable unsaturated compound (C) and an epoxy-containing long chain alkyl compound (D), whereby introducing the polymerizable unsaturated group and long chain alkyl group into said macromonomer (A), with
an ethylenically unsaturated monomer (B). (This resin is hereinafter referred to as xe2x80x9cpigment dispersing resin Vxe2x80x9d.)
The invention still further provides a pigment dispersing resin having a weight-average molecular weight within a range of 3,000-100,000 and a resin acid value within a range of 10-200 mgKOH/g, which is obtained by copolymerizing said macromonomer (A-1) with an ethylenically unsaturated monomer (B), and
subjecting the resulting copolymer (F) further to an esterification reaction with an epoxy-containing long chain alkyl compound (D). (This resin is hereinafter referred to as xe2x80x9cpigment dispersing resin VIxe2x80x9d.)
The invention also provides a water-based pigment dispersion which comprises at least one of above pigment dispersing resins I-VI, pigment, aqueous medium and a basic neutralizing agent, and if necessary a dispersion assistant.
The invention furthermore provides a water-based paint composition which comprises the above water-based pigment dispersion.
Hereafter we will explain in further details the pigment dispersing resins, water-based pigment dispersions and the water-based paint compositions, all according to the present invention.
The pigment dispersing resin I according to the invention consists of a copolymer of macromonomer (A) with an ethylenically unsaturated monomer (B) which are hereafter explained.
Macromonomer (A):
Macromonomer (A) is the monomer component which is characteristic of those pigment dispersing resins of the present invention, and is prepared by copolymerizing methacrylic acid with at least one copolymerizable monomer selected from the group consisting of methacrylic acid esters and styrene, in the presence of a metal complex which is a catalytic chain transfer agent or an addition cleavage-type chain transfer agent, and if necessary a radical polymerization initiator.
Where a catalytic chain transfer agent is used, the copolymerization is referred to as Catalytic Chain Transfer Polymerization, i.e., xe2x80x9cCCTP processxe2x80x9d.
CCTP processes are described, for example, in U.S. Pat. No. 4,694,054, U.S. Pat. No. 4,694,054, EP 712419 and U.S. Pat. No. 5,721,330, Macro-molecules, 1996, 29, 8083-8089, and any of these known CCTP processes can be used for preparing the macromonomer (A). That is, for carrying out the copolymerization by means of a catalytic chain transfer process, methacrylic acid and at least one copolymerizable monomer selected from methacrylic acid esters and styrene are subjected to, for example, solution polymerization in an organic solvent or emulsion polymerization in an aqueous medium, in the presence of a metal complex which is a catalytic chain transfer agent and a radical polymerization initiator.
As examples of the metal complex useful for said copolymerization, cobalt complex, iron complex, nickel complex, ruthenium complex, rhodium complex, palladium complex, rhenium complex and iridium complex may be named. Of those, cobalt complex is preferred because it acts as a catalytic chain transfer agent very effectively.
As useful cobalt complexes, those known per se from prior art references such as Hei 6 (1994)-23209B1-JP, Hei 7 (1995)-35411B1-JP, U.S. Pat. No. 4526945, U.S. Pat. No. 4,694,054, U.S. Pat. No. 4,837,326, U.S. Pat. No. 4,886,861, U.S. Pat. No. 5,324,879, WO 95/17435, and WO 95/25765 can be used, specific examples including bis(borondifluorodioxyiminocycloyhexane)Co (II), bis(1,2-dioxyiminoethane)Co (II), bis(borondifluorodimethylgyoximate)Co (II), bis(borondifluorodiphenylglyoximate)Co (II), cobalt (II) chelate of vicinal iminohydroxyimino compound, cobalt (II) chelate of diazadihydroxyiminodialkyldecadiene, cobalt (II) chelate of diazadihydroxyiminodialkylundecadiene, cobalt (II) chelate of tetraazatetraalkylcyclotetradecatetra-ene, cobalt (II) chelate of tetraazatetraalkylcyclotetradodecatetra-ene, cobalt (II) chelate of N,Nxe2x80x2-bis(salicylidene)ethylenediamine, cobalt (II) chelate of dialkyldiazadioxodialkyldodecadiene, cobalt (II) chelate of dialkyldiazadioxodialkyltridecadiene and cobalt (II) porphyrin complex and the like. Of these, readily available bis(borondifluorodimethylglyoximate)Co (II) and bis-(borondifluorodiphenylglyoximate)Co (II) are used with particular convenience.
Metal complexes in which radical cleavable groups are directly bound to metals, such as those described in WO 87/03605, can also be used as the catalytic chain transfer agent. Examples of the metals include cobalt, rhenium and iridium, and examples of radical cleavable groups include alkyl, aryl and heterocyclic groups. In the systems using such a metal complex in which a radical cleavable group is directly bound to a metal, concurrent use of a radical polymerization initiator is unnecessary.
The use rate of above metal complex serving as a catalytic chain transfer agent is not critical. Whereas, normally the suitable amount is within a range of from 1xc3x9710xe2x88x926 to 1 part by weight, preferably 1xc3x9710 xe2x88x924 to 0.5 part by weight, per 100 parts by combined weight of the methacrylic acid and at least one copolymerizable monomer selected from methacrylic acid esters and styrene.
For adjusting reactivity, or improving solubility, of the metal complex, a known coordination compound may be concurrently used, if required. Examples of useful coordination compound include phosphorus compounds such as triphenylphosphine and tributylphosphine; and amine compounds such as pyridine and tributylamine.
As the polymerization initiators useful for CCTP processes, the following may be named for example: organic peroxide polymerization initiators including ketone peroxides such as cyclohexanone peroxide, 3,3,5-trimethylcyclohexanone peroxide and methylcyclohexanone peroxide; peroxyketals such as 1,1-bis(tert-butylperoxy)-3,3,5-trimethylcyclohexane, 1,1-bis(tert-butylperoxy)cyclohexane and n-butyl-4,4-bis(tert-butylperoxy)valerate; hydroperoxides such as cumene hydroperoxide and 2,5-dimethylhexane-2,5-dihydroperoxide; dialkylperoxides such as 1,3-bis(tert-butylperoxy-m-isopropyl)benzene, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane, diisopropylbenzene peroxide and tert-butylcumyl peroxide; diacyl peroxides such as decanoyl peroxide, lauroyl peroxide, benzoyl peroxide and 2,4-di-chlorobenzoyl peroxide; peroxycarbonates such as bis(tert-butylcyclohexyl) peroxydicarbonate; and peroxy esters such as tert-butylperoxy-benzoate and 2,5-dimethyl-2,5-di(benzoylperoxy)hexane; and azo polymerization initiators including 2,2xe2x80x2-azobisisobutyronitrile, 1,1-azobis(cyclohexane-1-carbonitrile), azocumene-2,2xe2x80x2-azobismethylvaleronitrile and 4,4xe2x80x2-azobis(4-cyanovalerianic acid). The use rate of these polymerization initiators is not critical, while normally it is desirably within a range of 0.1-15 parts by weight, in particular, 0.3-8 parts by weight, per 100 parts by weight of the combined sum of the monomers to be copolymerized.
Where an addition-cleavable chain transfer agent is used in said copolymerization reaction, the copolymerization is performed by radical addition-cleavage type chain transfer process. As such addition-cleavage type chain transfer agent, 2,4-diphenyl-4-methyl-1-pentene (abbreviated as xe2x80x9cxcex1-methylstyrene dimerxe2x80x9d) can be named as an example. The use rate of such an addition-cleavage type chain transfer agent is not critical, but it is normally suitable to use 1-50 parts by weight, preferably 5-30 parts by weight, per 100 parts by weight of the total sum of the monomers to be copolymerized.
Where such radical addition cleavage-type chain transfer polymerization is conducted as the copolymerization reaction, the monomers can be polymerized by such means as solution polymerization in an organic solvent or emulsion polymerization in an aqueous medium, in the presence of an addition cleavage type chain transfer agent and optionally a radical polymerization initiator. As the radical polymerization initiator, any of those exemplified as the polymerization initiators useful for CCTP processes can be used.
Said macromonomer (A) is obtained by co-polymerizing a monomeric mixture of methacrylic acid and at least one copolymerizable monomer selected from methacrylic acid esters and styrene, by any of the processes as above-described. Specific examples of methacrylic acid esters include: linear, branched or cyclic C1-C24 alkyl esters of methacrylic acid such as methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, 2-ethylhexyl methacrylate, n-octyl methacrylate, lauryl methacrylate, stearyl methacrylate, cyclohexyl methacrylate, isobornyl methacrylate and tridecyl methacrylate; C2-C4 hydroxyalkyl esters of methacrylic acid such as 2-hydroxyethyl methacrylate, hydroxypropyl methacrylate, 2,3-dihydroxybutyl methacrylate and 4-hydroxylbutyl methacrylate; monoesterified compounds of polyhydric alcohol with methacrylic acid, such as polyethylene glycol monomethacrylate; and ring-opening polymerization products of said monoesterified products of polyhydric alcohol with methacrylic acid, with 2-caprolactone. These polymerizable unsaturated monomers can be used either singly or in combination of two or more.
The ratio of methacrylic acid to said at least one copolymerizable monomer selected from methacrylic acid esters and styrene is so selected that the resulting macromonomer should have an acid value within a range of 50-450 mgKOH/g, preferably 65-400 mgKOH/g, inter alia 65-300 mgKOH/g, which is normally 8-70%, preferably 10-60%, inter alia, 10-46% by weight, of methacrylic acid to 30-92%, preferably 40-90%, inter alia, 54-90% by weight, of the copolymerizable monomer(s), the percentages being based on the combined weight of all the monomer to be copolymerized.
As the polymerization method for obtaining the macromonomer (A), solution polymerization in an organic solvent, emulsion polymerization in an aqueous medium, and the like can be used as aforesaid, in particular, solution polymerization being preferred. In an embodiment of the solution polymerization, said monomeric components (methacrylic acid and at least one copolymerizable monomer selected from methacrylic acid esters and styrene); a metal complex which is the catalytic chain transfer agent, or an addition cleavage type chain transfer agent; and if necessary a radical polymerization initiator; are dissolved or dispersed in an organic solvent and are copolymerized under heating under stirring, normally at temperatures ranging from about 80xc2x0 C.-about 200xc2x0 C., for about 1-10 hours.
Examples of the useful organic solvent include hydrocarbon solvents such as heptane, toluene, xylne, octane and mineral spirit; ester solvents such as ethyl acetate, n-butyl acetate, isobutyl acetate, ethylene glycol monomethylether acetate and diethylene glycol monobutylether acetate; ketone solvents such as methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone and cyclohexanone; alcohol solvents such as methanol, ethanol, isopropanol, n-butanol, sec-butanol and isobutanol; ether solvents such as n-butyl ether, dioxane, ethylene glycol monomethyl ether and ethylene glycol monoethyl ether and the like; and aromatic petroleum solvents such as Swasol(trademark) 310, Swasol(trademark) 1000 and Swasol(trademark) 1500 of Cosmo Oil Co., Ltd. Those organic solvents can be used either singly or in combination of two or more. At the time of copolymerization, the organic solvent is normally used in an amount not more than 40 parts by weight based on the total weight of the monomer components to be copolymerized.
In the above copolymerization reaction, the method of addition of the components to be polymerized or the polymerization initiator is not critical. Whereas, the polymerization initiator is conveniently added dropwise plural times by portions over the time spun from the initial stage of polymerization to the advanced stage, rather than adding in a lump sum at the initial stage, for effective temperature control during the polymerization reaction and prevention of undesirable cross-linked product such as gel from forming.
So obtained macromonomer (A) has at least one polymerizable unsaturated bond, preferably only one polymerizable unsaturated bond, at one end of its molecule. From the standpoints of aqueous dispersion stability, pigment dispersion stability, viscosity, VOC and color number (extent of coloring) of the resin, the macromonomer (A) conveniently has a resin acid value within a range of 50-450 mgKOH/g, preferably 65-400 mgKOH/g, inter alia, 65-300 mgKOH/g. While the molecular weight of macromonomer (A) is not critical, it normally ranges, in terms of weight-average molecular weight, 300-15,000, preferably 500-10,000, in particular, 500-7,000.
Ethylenically Unsaturated Monomer (B)
As ethylenically unsaturated monomer (B) to be copolymerized with above macromonomer (A), methacrylic acid esters and styrene can be conveniently used. Methacrylic acid ester(s) can be suitably selected from those earlier enumerated as examples of methacrylic acid esters useful for the preparation of macromonomer (A). Also as the ethylenically unsaturated monomer (B) to be copolymerized with macromonomer (A), besides said at least one monomer selected from methacrylic acid esters and styrene, up to 30% by weight based on the total weight of the ethylenically unsaturated monomer (B) of other monomer or monomers may be used.
Examples of such other monomers include C1-C24 alkyl esters of acrylic acid such as methyl acrylate, ethyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, tert-butyl acrylate, 2-ethylhexyl acrylate and stearyl acrylate; C2-C4 hydroxyalkyl esters of acrylic acid such as 2-hydroxyethyl acrylate; aminoalkyl acrylates such as N,N-dimethylaminoethyl acrylate, N,N-diethylaminoethyl acrylate and N,N-dimethylaminopropyl methacrylate; (meth)acrylamides and their derivatives such as (meth)acrylamide, N,N-di-methylaminoethyl (meth)acrylamide, N,N-diethylaminoethyl (meth)-acrylamide, N-methylol (meth)acrylamide methyl ether and N-methylol (meth)acrylamide butyl ether; oxetane ring-containing (meth)acrylates such as 3-ethyl-3-(meth)acryloyloxymethyl oxetane and 3-methyl-3-(meth)acryloyloxymethyl oxetane; carboxyl-containing polymerizable unsaturated monomers such as methacrylic acid and acrylic acid; and (meth)acrylonitrile, vinyl acetate and vinyltoluene. These monomers may be used either singly or in combination of two or more.
Because the resins of the invention are intended to be used for water-based dispersions of pigment, their construction preferably is divided into hydophilic part and hydrophobic part, the latter acting for dispersing (adsorption of) the pigment and the former acting as a stabilizer in the water-based pigment dispersion paste or water-based paint.
According to the invention, in synthesizing the blocked pigment dispersing resin in which the hydophilic part and hydrophobic part are structurally regulated, the macromonomer (A) serves as the hydophilic component and the ethylenically unsaturated monomer (B) to be copolymerized therewith, as the hydrophobic component. Hence it is possible to effectively increase density of hydrophilicity by using the macromonomer, while increasing the ratio of the hydrophobic part which acts for pigment dispersing (adsorption).
Accordingly, it is desirable that the ethylenically unsaturated monomer (B) to be copolymerized with macromonomer (A) is a hydophobic monomer. Examples of preferred monomers include C1-C24 alkyl or cyclic alkyl esters of methacrylic acid such as methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, tert-butyl methacrylate, 2-ethylhexyl methacrylate, n-octyl methacrylate, lauryl methacrylate, stearyl methacrylate, cyclohexyl methacrylate, isobornyl methacrylate and tridecyl methacrylate; styrene and vinyltoluene. In particular, styrene and derivatives thereof, methyl methacrylate and 2-ethylhexyl methacrylate are preferred.
Whereas, it is permissible to copolymerize a minor amount of hydrophilic polymerizable unsaturated monomer, for stabilization of the hydrophobic component in water. Examples of useful hydrophilic polymerizable unsaturated monomer include carboxyl-containing polymerizable unsaturated monomers such as methacrylic acid and (meth)acrylamide and derivatives thereof such as methacrylamide, N-methylolmethacrylamide, N-methylolmethacrylamide methyl ether and N-methylolmethacrylamide butyl ether.
Copolymerization
The polymerization of macromonomer (A) with ethylenically unsaturated monomer (B) can be preformed, for example, following a radical polymerization process known per se, by copolymerizing macromonomer (A) with ethylenically unsaturated monomer (B) in the presence of a radical polymerization initiator, by means of solution polymerization in an organic solvent or emulsion polymerization in an aqueous medium.
The radical polymerization initiator can be suitably selected from those earlier named as radical polymerization initiators useful for the preparation of macromonomer (A).
The copolymerization ratio of the macromonomer (A) and ethylenically unsaturated monomer (B) is not subject to any strict limitation, but is variable depending on the desired properties for the resultant resin. Whereas, it is generally desirable that the two components are within the following ranges, based on the combined weight of the two monomers, the percentages being by weight:
macromonomer (A):
5-80 %, preferably 10-60%, inter alia, 10-50%
ethylenically unsaturated monomer (B):
20-95%, preferably 40-90%, inter alia, 50-90%.
Thus obtained pigment dispersing resin I can have a weight-average molecular weight within a range of 3,000-100,000, preferably 5,000-40,000, inter alia, 5,000-35,000; and a resin acid value within a range of 10-200 mgKOH/g, preferably 20-150 mgKOH/g, inter alia, 20-120 mgKOH/g.
The pigment dispersing resin II of the present invention consists of a copolymer obtained by copolymerization of macromonomer (A-1), which is obtained through an esterification reaction of earlier described macromonomer (A) with an epoxy-containing polymerizabe unsaturated compound (C) so that polymerizable unsaturated group(s) is (are) introduced into said macromonomer (A), with above-described ethylenicaly unsaturated monomer (B).
Epoxy-containing Polymerizable Unsaturated Compound (C)
The epoxy-containing polymerizable unsaturated compound (C) is a component for introducing polymerizable unsaturated group(s) into the macromonomer (A), utilizing the esterification reaction between the carboxyl group in macromonomer (A) and the epoxy group in the compound (C). The compound preferably contains, per molecule, one each of epoxy group and polymerizable unsaturated group (e.g., an ethylenic double bond).
Examples of such epoxy-containing unsaturated compound (C) include: glycidyl (meth)acrylate, 3,4-epoxycyclohexyl (meth)-acrylate, xcex2-methylglycidyl (meth)acrylate and allylglycidyl ether. Of those, glycidyl methacrylate is preferred.
The quantitative ratio of the epoxy-containing unsaturated compound (C) to macromonomer (A) in said esterification reaction is not strictly limited. Whereas, from the standpoints of controlling the molecular weight of the ultimately formed resin and inhibition of viscosity increase or gellation of the copolymerization reaction system with the ethylenically unsaturated monomer (B), it is generally convenient to use 0.5-15 parts, preferably 1-10 parts, inter alia, 1-8 parts by weight, of the epoxy-containing unsaturated compound (C), per 100 parts by weight of the solid component of macromonomer (A). It is furthermore desirable that the total amount of the polymerizable unsaturated groups in the macromonomer (A-1) formed through said esterification reaction is, on average 0.01-3, preferably 0.05-2.5, inter alia 0.05-2, per molecule.
The esterification reaction of macromonomer (A) with the epoxy-containing unsaturated compound (C) can be performed in the normal manner, for example, by adding an organic solvent to macromonomer (A) if necessary, and reacting the same with said epoxy-containing unsaturated compound (C) at temperatures ranging from about 100 to about 150xc2x0 C. It is desirable in that occasion to use a tertiary amine such as N,N-dimethyllaurylamine or N,N-dimethyl-dodecylamine as catalyst and concurrently a polymerization inhibitor such as 4-tert-butylpyrocatechol.
Copolymerization
The so obtained macromonomer (A-1) into which a polymerizable unsaturated group(s) are introduced can provide a pigment dispersing resin (II) of the invention, upon copolymerization with the ethylenically unsaturated monomer (B). This copolymerization can be performed in the same manner to that of the macromonomer (A) with the ethylenically unsaturated monomer (B) to prepare the pigment dispersing resin I, except that macromonomer (A-1) is used in place of macromonomer (A).
The macromonomer (A-1) being a so called poly-vinyl macromonomer into which polymerizable unsaturated group(s) are introduced, the formed copolymer takes a branched structure and its molecular weight also is large.
Thus obtained pigment dispersing resin II can have a weight-average molecular weight within a range of 5,000-100,000, preferably 7,000-70,000, inter alia, 7,000-60,000, and a resin acid value within a range of 10-200 mgKOH/g, preferably 20-150 mgKOH/g, in particular, 20-120 mgKOH/g.
The pigment dispersing resin III of the present invention consists of a copolymer obtained by copolymerization of macromonomer (A-2) into which a long chain alkyl group has been introduced, with above-described ethylenically unsaturated monomer (B), said macromonomer (A-2) having been prepared by subjecting the earlier described macromonomer (A) to an esterification reaction with an epoxy-containing long chain alkyl compound (D).
Epoxy-Containing Long Chain Alkyl Compound (M)
The epoxy-containing long chain alkyl compound (D) is a component for introducing a long chain alkyl group into said macromonomer (A), utilizing the esterification reaction between the carboxyl group in the macromonomer (A) and the epoxy group in the compound (D). As such, a compound containing, per molecule, one epoxy group and at least one, preferably only one, long chain alkyl group can be used. Here the long chain alkyl group may be either linear or branched, and those containing 6-24, preferably 8-20, inter alia, 8-16 carbon atoms are convenient.
Examples of such epoxy-containing long chain alkyl compounds include: 2-ethylhexylglycidyl ether, Cardura(trademark) E10 (Shell Chemicals Co., Ltd., a glycidyl ester of C9-C11 branched higher fatty acid).
The quantitative ratio of the epoxy-containing long chain alkyl compound (D) to macromonomer (A) in said esterification reaction is not critical. Whereas, from the standpoint of pigment dispersing property, it is generally convenient to use 2-60 parts, preferably 5-50 parts, inter alia, 5-40 parts by weight of said compound (D) per 100 parts by weight of the solid component of macromonomer (A). It is furthermore desirable that the long chain alkyl group content of macromonomer (A-2) formed upon the esterification reaction is, on average 0.01-3, preferably 0.05-2.5, inter alia, 0.05-2, per molecule.
The esterification reaction between macromonomer (A) and said epoxy-containing long chain alkyl compound (D) can be performed following any ordinary method, for example, through the steps of adding an organic solvent to macromonomer (A) if necessary, and reacting the same with said epoxy-containing long chain alkyl compound (D) at temperatures ranging from about 100 to about 150xc2x0 C. It is preferred to use a tertiary amine such as N,N-dimethyl-laurylamine or N,N-dimethyldodecylamine as a catalyst in that occasion.
Copolymerization
The so obtained macromonomer (A-2) into which a long chain alkyl group has been introduced can provide the pigment dispersing resin (III) of the present invention, when copolymerized with earlier described ethylenically unsaturated monomer (B). This copolymerization can be performed in the same manner to that of the macromonomer (A) with the ethylenically unsaturated monomer (B) to prepare the pigment dispersing resin I, except that macromonomer (A-2) is used in place of macromonomer (A).
Thus obtained pigment dispersing resin III can have a weight-average molecular weight within a range of 3,000-100,000, preferably 5,000-50,000, inter alia, 5,000-40,000, and a resin acid value within a range of 10-200 mgKOH/g, preferably 20-150 mgKOH/g, in particular, 20-120 mgKOH/g.
Because this pigment dispersing resin III contains a long chain alkyl group which is useful for improving pigment-wetting property, it is particularly suitable for dispersing strongly hydrophobic pigment such as phthalocyanin blue or for preparation of pigment dispersions of high pigment concentration.
Pigment Dispersing Resin IV
The pigment dispersing resin IV of the present invention is obtained through the steps of copolymerizing aforesaid macromonomer (A) with earlier described ethylenically unsaturated monomer (B) to form a copolymer (E), and subjecting said copolymer (E) to an esterification with aforesaid epoxy-containing long chain alkyl compound (D).
That is, the pigment dispersing resin IV has a structure of the pigment dispersing resin I into which a long chain alkyl group is further introduced utilizing the esterification reaction between the carboxyl group in said resin I and the epoxy group in said compound (D).
The copolymerization of macromonomer (A) with ethylenically unsaturated monomer (B) can be performed in the identical manner with the preparation of a pigment dispersing resin I. The resulting copolymer (E) conveniently has a weight-average molecular weight normally within a range of 3,000-100,000, preferably 5,000-70,000, inter alia. 5,000-60,000, and a resin acid value within a range of normally 10-200 mgKOH/g, preferably 20-150 mgKOH/g, inter alia, 20-120 mgKOH/g.
The esterification reaction of said copolymer (E) with an epoxy-containing long chain alkyl compound (D) can be performed in the manner similar to the esterification reaction between a macromonomer (A) and an epoxy-containing long chain alkyl compound (D) in the course of preparing above pigment dispersing resin III. In this esterification reaction, it is convenient to use the epoxy-containing long chain alkyl compound (D) at a ratio of normally 2-60 parts, preferably 5-50 parts, inter alia, 5-40 parts by weight, per 100 parts by weight of the copolymer (E)(in terms of solid content).
The resulting pigment dispersing resin IV can have a weight average molecular weight within a range of 3,000-100,000, preferably 5,000-50,000, inter alia 5,000-40,000, and a resin acid value within a range of normally 10-200 mgKOH/g, preferably 20-150 mgKOH/g, inter aha, 20-120 mgKOH/g.
The pigment dispersing resin IV contains a long chain alkyl group which is useful for improving pigment wetting property, similarly to pigment dispersing resin III, and therefore is particularly suitable for dispersing strongly hydrophobic pigment or preparing high concentration pigment dispersions.
The pigment dispersing resin V of the present invention consists of a copolymer of a macromonomer (A-3), into which a polymerizable unsaturated group and long chain alkyl group have been introduced, with said ethylenically unsaturated monomer (B), said macromonomer (A-3) having been obtained through an esterification reaction of earlier described macromonomer (A) with an epoxy-containing polymerizable unsaturated compound (C) and an epoxy-containing long chain alkyl compound (D).
Said esterification among the macromonomer (A) and the compounds (C) and (D) can be performed in the manner as earlier described, in which occasion the compounds (C) and (D) may be reacted with macromonomer (A) either simultaneously or sequentially in any optional order.
The quantitative ratios of the compounds (C) and (D) to macromonomer (A) are not critical. Whereas, from the standpoints of suitable molecular weight of the formed resin and its pigment dispersing property, it is convenient to use them within the ranges of, per 100 parts by weight of the solid content of the used macromonomer (A),
compound (C): normally 0.5-15, preferably 1-10, inter alia, 1-8, parts by weight, and
compound (D): normally 2-40, preferably 5-35, inter alia, 5-30, parts by weight.
Also said macromonomer (A-3) obtained by this esterification desirably contains on average 0.01-3, preferably 0.05-2.5, inter alia, 0.05-2 polymerizable unsaturated groups; and also normally 0.01-3, preferably 0.05-2.5, inter alia, 0.05-2 long chain alkyl groups, per molecule.
Said copolymerization of macromonomer (A-3) with ethylenically unsaturated monomer (B) can be performed in the same manner to that of the macromonomer (A) with the ethylenically unsaturated monomer (B) except that macromonomer (A-3) is used in place of macromonomer (A).
Thus obtained pigment dispersing resin V has a weight-average molecular weight within a range of 3,000-100,000, preferably 5,000-50,000, inter alia, 5,000-40,000, and a resin acid value within a range of 10-200 mgKOH/g, preferably 20-150 mgKOH/g, inter alia, 20-120 mgKOH/g.
The pigment dispersing resin VI of the present invention is obtained through the steps of subjecting aforesaid macromonomer (A) and the epoxy-containing polymerizable unsaturated compound (C) to an esterification reaction; copolymerizing the resulting macromonomer (A-1), into which the polymerizable unsaturated group is introduced, with the ethylenically unsaturated monomer (B); and further subjecting the resulting copolymer (F) and the epoxy-containing long chain alkyl compound (D) to an esterification reaction.
That is, this pigment dispersing resin VI has the structure of the earlier described pigment dispersing resin II into which further a long chain alkyl group is introduced by means of the esterification reaction between the carboxyl group contained in said resin II and the epoxy group contained in the compound (D).
Said esterification reaction of macromonomer (A) with the compound (C), and the copolymerization of the resulting macromonomer (A-1) with the monomer (B) can be performed in the identical manner with those steps in the preparation of the pigment dispersing resin II. Thus obtained copolymer (F) desirably has a weight-average molecular weight within a range of 3,000-100,000, preferably 5,000-70,000, inter alia, 5,000-60,000; and a resin acid value within a range of normally 10-200 mgKOH/g, preferably 20-150 mgKOH/g, inter alia, 20-120 mgKOH/g.
The esterification reaction of such copolymer (F) and the compound (D) can be performed in the similar manner to the esterification reaction of macromonomer (A) with the compound (I)) for preparing the pigment dispersing resin III. In said esterification reaction, preferably the epoxy-containing long chain alkyl compound (D) is used within a range of normally 2-40, in particular, 5-35, inter alia 5-30, parts by weight per 100 parts by weight of the copolymer (F).
The resulting pigment dispersing resin VI can have a weight average molecular weight within a range of 3,000-100,000, preferably 5,000-50,000, inter alia 5,000-40,000; and a resin acid value within a range of normally 10-200 mgKOH/g, preferably 20-150 mgKOH/g, inter alia, 20-120 mgKOH/g.
Water-Based Pigment Dispersions
Those pigment dispersing resins as above described show little expansion in solvent probably because they have blocked structures This is a very substantial advantage over straight chain (random) resins or graft resins, particularly for making low viscosity pigment paste. Again as aforesaid, because they are structure-regulated polymers divided into hydrophobic part and hydrophilic part, they exhibit markedly excelling pigment dispersing property (color developing property).
Furthermore, those pigment dispersing resins III-VI, into which long chain alkyl groups are introduced, excel in pigment wetting property and are useful for preparing high concentration pigment dispersions without inviting objectionable increase in their viscosity.
Those pigment dispersing resins II, V and VI have branched resin structures and are more apt to be branched or to have higher molecular weight than the pigment dispersing resins I, III and IV, and hence can enhance the action of steric repelling layer to prevent agglomeration of pigment. This is advantageous for pigment dispersing property (color developing property). Whereas, a higher molecular weight leads to a higher viscosity and in this respect those resins are somewhat inferior to the other pigment dispersing resins I, III and IV, for providing high concentration pigment dispersions (i.e., reduction of VOC).
As above, those pigment dispersing resins of the present invention are useful for preparing pigment dispersions.
A pigment dispersion can be prepared by blending, with at least one of the pigment dispersing resins of the invention, pigment, aqueous medium and a basic neutralizer, and if necessary a dispersion assistant and the like.
Examples of pigment include: bright pigments such as aluminium powder, copper powder, nickel powder, stainless steel powder, chromium powder, micaceous iron oxide, titanium dioxide-coated mica powder, iron oxide-coated mica powder and bright graphite; organic red pigments such as Pink EB, azo- and quinacridone-derived pigments; organic blue pigments such as cyanin blue and cyanin green; organic yellow pigments such as benzimidazolone-, isoindolin- and quinophthalone-derived pigments; inorganic colored pigments such as titanium white, titanium yellow, iron red, carbon black, chrome yellow, iron oxide; and various baked pigments. Blend ratios of these pigments are not subject to specific limitations, while they are normally within a range of 10-3,000, preferably 15-2,000, inter alia 15-1,500 parts, per 100 parts of a pigment dispersing resin or resins of the present invention, parts being by weight, in consideration of the pigment dispersing ability, dispersion stability and color developing property of resulting pigment dispersions.
Examples of useful aqueous medium include water and water-organic solvent mixtures formed by dissolving organic solvent such as water-soluble organic solvent in water. Useful organic solvent in such mixtures include, for example, water-soluble organic solvents such as methyl alcohol, ethyl alcohol, isopropyl alcohol propylpropylene glycol, butyl cellosolve, propylene glycol monomethyl ether and 3-methyl-3-methoxybutanol; and difficultly water-soluble or water-insoluble organic solvents such as xylene, toluene, cyclohexanone, hexane and pentane. Those organic solvents may be used either singly or as a mixture of two or more. Water-insoluble organic solvent may be concurrently used with water-soluble organic solvent, in minor quantities. The mixing ratio of water and organic solvent is not critical while it is desirable that the organic solvent content of the mixture does not exceed 50% by weight, in particular, 35% by weight. The blend ratio of the aqueous medium is not critical, while it is desirable that it is within a range of 50-5,000, preferably 100-3,000, inter alia, 100-2,000, parts by weight per 100 parts by weight of a pigment dispersing resin or resins of the present invention, in respect of viscosity in the occasion of dispersing the pigment, pigment dispersing ability, dispersion stability and production efficiency.
Said basic neutralizer acts to neutralize carboxyl groups in the pigment dispersing resin of the present invention to make the resin water-soluble or water-dispersible. Specific examples include inorganic bases such as ammonium hydroxide, sodium hydroxide and potassium hydroxide; and amines such as aminomethyl propanol, aminoethylpropanol, dimethylethanolamine, triethylamine, diethylethanolamine, dimethylaminopropanol and aminomethylpropanol. The use rate of such a basic neutralizer should be sufficient to render the pigment dispersing resin in individual blend composition water-soluble or water-dispersible. It is normally convenient, therefore, to use it at a rate sufficient to make the carboxyl neutralization equivalent in the pigment dispersing resin of the invention 0.3-1.5, preferably 0.4.-1.3.
As examples of dispersion assistant to be used if necessary, Disperbyk(trademark) 184 or 190 (BYK-Chemie Co.) may be named. Other usable additives include defoaming agent, antiseptic, rust-proofing agent and plasticizing agent. It is desirable that blend ratio of any of those additives does not exceed 50 parts per 100 parts of the pigment dispersing resin of the present invention, parts being by weight, in respect of pigment dispersing ability of the resin and stability of the pigment paste.
Those pigment dispersions can be formulated by homogeneously mixing and dispersing the above described constituents with a dispersing machine such as paint shaker, sand grind mill, ball mill, LMZ mill, DPC pearl mill and the like.
Water-Based Paint Compositions
Thus prepared pigment dispersion can be blended with binder resin for paint and suitably with other additives such as aqueous medium, fine polymer particles, curing catalyst, basic neutralizer, ultraviolet absorber, ultraviolet stabilizer, paint film surface regulating agent, antioxidant, flow property regulator, silan coupling agent and the like, and stably dispersed in the aqueous medium to provide a water-based paint composition.
Useful paint binder resins include combination of substrate resins which are normally used in the field of water-soluble or water-dispersible paint, with curing agent. Examples of such substrate resin include hydroxyl-containing acrylic resin, hydroxyl-containing polyester resin, epoxy-containing copolymer resin and carboxyl-containing high acid value resin. As examples of useful curing agent, amino resins and optionally blocked polyisocyanate compounds can be named, which can be used either singly or in combination.
As said hydroxyl-containing acrylic resin, copolymers having a weight-average molecular weight within a range of from about 2,000 to about 100,000, in particular, from 5,000 to 50,000, which are obtained by copolymerization of a hydroxyl-containing polymerizable unsaturated monomer such as 2-hydroxyethyl(meth)-acrylate with other polymerizable unsaturated monomer or monomers in the presence of a radical polymerization initiator are preferred.
As hydroxyl-containing polyester resin, those having a weight-average molecular weight within a range of from about 1,000 to about 100,000, in particular, from 1,500 to 70,000, which are obtained by condensation reaction between polyhydric alcohols such as ethylene glycol, butylene glycol, 1,6-hexanediol trimethylolpropane and pentaerythritol, and polyvalent carboxylic acids such as adipic acid, isophthalic acid, terephthalic acid, phthalic anhydride, hexahydrophthalic anhydride and trimellitic anhydride are preferred.
As amino resins which are used as curing agent, melamine resins are used in general, in particular, methylolmelamine resins and melamine resins whose methylol groups are at least partially etherified with C1-C4 monohydric alcohols are suitable. While it is preferred that they be water-soluble or water-dispersible, water-insoluble ones can also be used.
As commercially available melamine resins useful for the above purpose, the following may be named for example: butyl etherified melamine resins such as U-van(trademark) 20SE-60 and 225 (Mitsui Chemical, Co.), Super Beckamine(trademark)G840 and G821 (Dainippon Ink and Chemicals, Inc.); methyl etherified melamine resins such as Sumi-mal(trademark) M-100, M-40S and M-55 (Sumitomo Chemical Co., Ltd.), Cymel(trademark) 303, 325, 327, 350 and 370 (Mitsui Cytec Co., Ltd.), Nikalac(trademark) MS17 and MS15 (Sanwa Chemical Co., Ltd.) and Resimine(trademark) 741 (Monsanto Co.); methyl- and iso-butyl-mixed etherified melamine resins such as Cymel(trademark) 235, 202, 238, 254, 272 and 1130 (Mitsui Cytec Co., Ltd.), and Sumimalm(trademark) M66B (Sumitomo Chemical Co., Ltd.); and methylxe2x80x94and n-butyl-mixed etherified melamine resins such as Cymel(trademark) XV805 (Mitsui Cytec Co., Ltd.) and Nikalac(trademark) MS95 (Sanwa chemical Co., Ltd.).
Said optionally blocked polyisocyanate compounds usable as the curing agent include both of polyisocyanate compounds having free isocyanate groups and those in which isocyanate groups are blocked.
Examples of polyisocyanate compounds having free iso-cyanate groups include organic polyisocyanates per se, e.g., aliphalic diisocyanates such as hexamethylenediisocyanate and trimethylhexamethylenediisocyanate; cycloaliphatic diisocyanates such as hydrogenated xylylenediisocyanate and isophoronediisocyanate; aromatic diisocyanates such as tolylenediisocyanate and 4,4xe2x80x2-diphenylmethane-diisocyanate; and polyisocyanate compounds having no less than 3 isocyanate groups such as triphenylmethane-4,4xe2x80x2,4xe2x80x3-triisocyanate, 1,3,5-triisocyanatebenzene, 2,4,6-triisocyanatetoluene and 4,4xe2x80x2-dimethyldiphenylmethane-2,2xe2x80x2,5,5xe2x80x2-tetraisocyanate. Those organic polyisocyanates may be used in such forms as adducts with polyhydric alcohol, low molecular weight polyester resin, water or the like; or cyclic polymers between those organic polyisocyanates, or isocyanate biuret.
As commercially available polyisocyanate compounds having free isocyanate groups, for example, Burnock(trademark) D-750, -800, DN-950, DN-970 and DN-15-455 (Dainippon Ink and Chemicals, Inc.); Desmodur(trademark) L, N, HL and N3390 (Sumitomo Bayer Urethane Co., Ltd.; Takenate(trademark) D-102, -202, -110 and -123N (Takeda Chemical Industries, Ltd.); Coronate(trademark) EH, L, HL and 203 (Nippon Polyurethane Industry Co., Ltd.); and Duranate(trademark) 24A-90CX (Asahi Chemical Industry Co., Ltd.) may be named.
As polyisocyanate compounds in which isocyanate groups are blocked, those formed by blocking isocyanate groups in the above-described polyisocyanate compounds having free isocyanate groups, with a known blocking agent such as oxime, phenol, alcohol, lactam, malonic acid ester or mercaptane can be used. Typical commercially available polyisocyanate compounds whose isocyanate groups are blocked include Burnock(trademark) D-550 (Dainippon Ink and Chemicals, Inc.), Takenate(trademark) B-815-N (Takeda Chemical Industries, Ltd.), Additol(trademark) VXL-80 (Hoechst AG, Germany), Coronate(trademark) 2507 (Nippon Polyurethane Industry Co., Ltd.) and Desmodur(trademark) N3500 (Sumitomo Bayer Urethane Co., Ltd.).
The aqueous medium which is used when necessity arises can be suitably selected from those useful for preparing the pigment dispersions as earlier explained.
The fine polymer particles are provided by a polymer which does not dissolve in water-based paint compositions of the present invention but disperses as fine particles. Suitable average particle size normally is within a range of 0.01-1 xcexcm, preferably 0.05-0.8 xcexcm. Inside of the particles may either be crosslinked or not, the former being preferred. As such fine polymer particles, those known per se as flow property regulator in the field of paint can be used.
Where an optionally blocked polyisocyanate compound is used as the curing agent, organometal catalysts such as dibutyltin diacetate, dibutyltin dioctate, dibutyltin dilaurate and the like; and amines such as triethylamine, diethanolamine and the like can be conveniently used as the curing catalyst. Whereas, an amino resin such as melamine resin is used as the curing agent, such curing catalyst as sulfonic acid compound, e.g., paratoluenesulfonic acid, dodecylbenzensulfonic acid and dinonylnaphthalenesulfonic acid; or amine-neutralization products of these sulfonic acid compounds are conveniently used.
As examples of ultraviolet absorber, benzophenone, benzotriazole, cyanoacrylate, salicylate and oxalic acid anilide compounds may be named. As the ultraviolet stabilizer, hindered amine compounds can be used.
The water-based paint compositions according to the invention are useful as coloring paint compositions (including metallic paint and iridescent paint) into which various pigments such as coloring pigments, metallic pigments and iridescent pigments are blended. In particular, they can be conveniently used for automotive finish.
The paint compositions according to the invention can be applied onto various object matters to be coated (painted), following the practice known per se, and can form cured coating film when baked normally at temperatures of from about 80xc2x0 C. to about 180xc2x0 C., for about 10-60 minutes. Where a short time baking is desired, for example, a cured coating film can be formed by baking under such conditions as will attain the highest temperature of from about 180xc2x0 C. to about 250xc2x0 C. of the material being baked, for about 20-about 60 seconds.
The matters to be painted with the paint compositions of the present invention are subject to no specific limitation, examples of which including metallic substrate such as steel sheet, aluminium, tin and the like; other substrate such as of mortar, cement, plastics, glass and the like; and those substrates which have been surface treated and/or applied with coating film. In particular, metallic substrates and plastic substrates are suitable for use.
Examples of steel sheet include cold-rolled steel sheet, molten galvanized steel sheet, electrogalvanized steel sheet, aluminum plated steel sheet, stainless steel sheet, copper plated steel sheet, tin plated steel sheet, lead-tin alloy plated steel sheet (turn sheet); steel sheet plated with zinc alloy such as iron-zinc, aluminium-zinc, nickel-zinc alloys and the like. As surface-treated steel sheet, for example, steel sheet which is given a chemical treatment such as phosphate treatment, chromate treatment and the like may be named.
As the substrate on which coating film has been formed, a substrate which has been optionally surface treated and thereafter primer-coated, or said substrate which is further applied with an inter-coat can be used.
When a paint composition according to the present invention is used for automotive finish, typical object matters to be coated include: a chemically treated steel sheet which is further electrodeposition-coated with primer and optionally applied with an inter coat thereon; various plastic substrates (which have been optionally surface treated, brimer-coated or further applied with an inter coat); and composite members which are combination of the foregoing.
The electrodepositing paint for electrodeposition coating may be anionic or cationic, cationic type being preferred because of good corrosion resistance. As cationic electrodeposition paint, any of those known per se can be used. For example, those containing as the resin component a base resin having hydroxyl groups and cationic groups and as the curing agent a blocked polyisocyanate compound can be conveniently used.
The water-based paint compositions according to the present invention are conveniently used for colored coating film-forming compositions for 1-coat-1-bake finish of object substrates, and for top coating colored base paint compositions in 2-coat-1-bake (2C1B), 2-coat-2-bake (2C2B), 3-coat-1-bake (3C1B), 3-coat-2-bake (3C2B), or 3-coat-3-bake (3C3B) systems.
Where the paint compositions according to the present invention are used for colored top coating for automobiles, the top coat can be formed through the steps of, applying the paint composition onto a primer film such as an electrodeposited coating film or onto an uncured or cured inter coat applied onto such a primer film, by such means as electrostatic coating (bell-type or the like) or aerosol coating, to a dry film thickness of normally from about 10 to about 60 xcexcm; and allowing it to stand for several minutes at room temperature, or forcedly drying the film for several minutes at temperatures ranging from about 50xc2x0 to about 80xc2x0 C.; thereafter applying a clear top coat paint thereon; and baking the same at temperatures of from about 120xc2x0 to about 180xc2x0 C. normally for about 10-about 60 minutes. It is also possible to apply a clear top coating paint onto the uncured or cured colored top coat film, by such means as electrostatic coating (bell-type or the like) or aerosol coating, to a dry film thickness of normally from about 20 to about 100 xcexcm followed by curing, to form multi-layered top coating film.
As such clear top coating paint to be applied onto the above-described colored top coat, those conveniently used are clear top coating paints comprising at least one base resin having a crosslinkable functional group (e.g., hydroxyl epoxy, carboxyl, alkoxysilane group and the like) such as acrylic, vinyl, polyester, alkyd and urethane resins; and at least one crosslinking agent for crosslinking and curing the base resin, such as alkyletherified melamine resin, urea resin, guanamine resin, optionally blocked polyisocyanate compound, epoxy resin and carboxyl-containing compound. In such clear top coating paint, convenient blend ratio of the base resin and the cross-linking agent is, based on the sum of the two components, normally 50-90% by weight of the base resin component and 10-50% by weight of the cross-linking agent component.
The form of such clear top coating paint is subject to no specific limitation and it can take any desired form such as organic solvent type, non-aqueous liquid dispersion type, aqueous solution type, aqueous dispersion (slurry) type, high solid type or powder type.
Hereinafter the invention is explained in further details, referring to production examples, working examples and comparative examples, in which parts and percentages are by weight unless otherwise specified.